We ran a batch of 1,200 ANSI 150# carbon steel pipe flanges for an oil and gas customer earlier this year. Each flange needed a bolt hole circle drilled to a specific pattern — eight 3/4″ through-holes at a 9.5″ bolt circle diameter. That’s nearly 10,000 holes total, so efficiency mattered a lot on this one.
We set up a dedicated drill fixture on our radial arm drill press, which let us index the part quickly without re-indicating between holes. We used a cobalt jobber-length drill with a split-point tip to keep the entry clean without a center drill. Coolant was sulphur-based cutting oil applied by brush — old school, but it works great on mild steel.
Drill life was excellent — we changed bits every 150 parts. Hole location was checked every 50 parts with a simple go/no-go pin gauge. All flanges shipped on time, and none came back for rework. Sometimes the straightforward jobs are the most satisfying.